1. Field of the Invention
The present invention relates generally to an automotive suspension control system which actively controls suspension characteristics for adjusting vehicular attitude. More specifically, the invention relates to an actively controlled vehicular suspension system which features anti-roll control.
2. Description of the Background Art
The U.S. Pat. No. 4,702,490, issued on Oct. 27, 1987, to Hirotsugu YAMAGUCHI et al., and assigned to the common assignee to the present invention, discloses an actively or positively controlled automotive suspension system which includes hydraulic cylinder for generating variable damping force against relative motion of a vehicular suspension member and a vehicle body in bounding and rebounding directions for adjusting suspension characteristics and adjusting vehicle body attitude.
Similar type actively controlled suspension systems has been disclosed in the co-pending U.S. patent application Ser. No. 060,911, filed on June 12, 1987 and assigned to the common assignee to the present invention. Further, European Patent First Publication Nos. 02 49 246 and 02 49 209 respectively corresponding to co-pending U.S. patent applications Ser. Nos. 061,368 (filed on June 15, 1987) and 059,888, filed on June 9, 1987, both of which have been assigned to the common assignee to the present invention. The later-mentioned three inventions includes features of anti-roll suspension control for adjusting damping characteristics at respective vehicular wheel for suppressing vehicular rolling motion.
Generally, anti-roll suspension control in this type of actively controlled suspension system, is performed in terms of lateral acceleration to be exerted on the vehicle body. In order to satisfactorily suppress vehicular rolling, it is required to provide sufficient gain for a lateral acceleration dependent control loop. However, on the other hand, greater gain in the control loop tends to increase magnitude of self-induced vibration in rolling direction. Therefore, for minimizing or maintaining the self-induced vibration magnitude within an acceptable level, the gain of the control loop has to be limited. The limited loop gain in the control loop tends to make anti-roll characteristics of the suspension system unsatisfactory.
On the other hand, it is noted by the inventor of the present invention that uncomfortable self-induced vibration tends to occur at substantially low vehicle speed range. It is also found that magnitude of self-induced vibration becomes smaller or self-induced vibration will not affect for riding comfort at higher vehicle speed.